In recent years, there have been proposed and developed various idling-stop system equipped vehicles or automatic engine stop-restart system equipped hybrid vehicles for improved fuel economy. Such a system often uses an electric-motor-driven oil pump in order to prevent a drop in hydraulic pressure in an oil supply line connected to an automatic transmission by temporary hydraulic-pressure supply to the transmission by means of the electric-motor-driven oil pump, even when a mechanical oil pump has been kept in its stopped state at an automatic engine-stop mode. When the electric-motor-driven oil pump is unfailed and normally operating, as a matter of course, the transmission can be operated normally by hydraulic pressure discharged from the electric-motor-driven oil pump. On the contrary, when the electric-motor-driven oil pump does not normally discharge hydraulic pressure, the transmission cannot be normally operated.
That is, it is very important to determine whether there is an abnormality in the automatic-transmission hydraulic system containing the electric-motor-driven oil pump as well as the mechanical oil pump. One such abnormality-check system equipped automatic engine stop-restart control system has been disclosed in Japanese Patent Provisional Publication No. 2004-68732 (hereinafter referred to as JP2004-068732), corresponding to U.S. Pat. No. 6,913,558. In the automatic engine stop-restart control system (the electric-motor-driven oil pump system) disclosed in JP2004-068732, under an automatic engine-stop state, as control parameters, a line pressure in a supply line provided for supplying hydraulic pressure from an electric-motor-driven oil pump to an automatic transmission and a motor current of the pump motor are detected. For instance, when the line pressure, detected under an automatic engine-stop state, reduces to below a predetermined pressure value, or when the motor current, detected under an automatic engine-stop state, is outside of a given motor-current range, the automatic engine-stop mode is canceled (disabled or inhibited) and in lieu thereof an automatic engine-restart mode is enabled.